Recently, attention is being focused on network systems in which multiple electrical household appliances are connected by cables for transmission and reception of voice and image data. For example, it is now common to watch videos shot with a digital video camera by connecting the camera to a monitor by cables, or to edit images by connecting the camera to a video apparatus. More recently, there is a trend of building such network systems not with cables but wirelessly. Wireless transmission and reception provides an advantage in that the troublesome aspects of wiring devices can be eliminated. An example of such a wireless network (to be referred to as a wireless bus) will be described below.
FIG. 32 shows a block diagram of a configuration of terminals and a hub station in a wireless bus. Numeral 1 designates a wireless bus (wireless network), 2 a hub station, and 3–6 nodes formed by multiple terminals. The wireless bus 1 includes a plurality of devices called nodes, and multimedia data is transmitted and received among the nodes. The transmission and reception of the data are managed by the hub station 2. In order to enable inter-node wireless communication, the nodes 3 to 6 in the wireless bus 1 have memory regions for storing node configuration information concerning the wireless bus 1, node information about each node, and inter-node communication quality information. The hub station 2 is selected from those of the nodes 3 to 6 in the wireless bus 1 that have the functions required of a hub station. One prerequisite for a node to become the hub station 2 is that the node be located at a position that allows it to communicate with every other node in the wireless bus 1. The hub station 2 is also required to have functions for gathering and analyzing the node configuration information, node information for each node, and inter-node communication quality information transmitted from the nodes 3 to 6, so that it can manage the latest information.
Hereafter, the node configuration information, node information, and inter-node communication quality information managed by the hub station 2 will be described.
The node configuration information indicates whether or not the individual nodes 3 to 6, which are centrally managed by the hub station 2, can carry out communication. When there is a change in the node configuration in the wireless bus 1, such as when a node is newly registered or deleted, the node configuration information is updated. The node information indicates the function of each node. Of the nodes participating in the wireless bus 1, some have the functions of the hub station 2, some have relay capability, and some have only an asynchronous communication function. In order to build the wireless bus 1, it is necessary to check the functions of the individual nodes and then select a hub station from among the nodes having a management function.
The node configuration information and the node information are updated only when a node is newly registered or deleted in the wireless bus 1, or the function of a node is changed. These items of information are not modified for any other reason.
The communication quality information indicates the states of communication condition between individual nodes when data is transmitted or received wirelessly. When a wireless bus is constructed in a wireless environment, it is necessary to select an appropriate transmission method adapted to the conditions of communication paths, so that accurate transmission and reception can take place. However, a wireless transmission path could deteriorate when a node has been transported or when there are people or obstacles located between two nodes, for example, making it impossible to transmit or receive data. Thus, the communication path conditions among the individual nodes vary on a case-by-case basis, and so the hub station must receive the communication path conditions from the nodes and manage them.
As an example of the method of managing the information mentioned above, JP Patent Publication (Unexamined Application) No. 11-88396 discloses an apparatus for managing node configuration information in a network of a plurality of nodes connected by cables. In this example, each node carries a table for the management of the node configuration information in the network. Each time the node configuration is updated, the node configuration information is transmitted to other nodes, so that there are no discrepancies regarding the node configuration information carried by the individual nodes in the network. This example is wired and involves only node configuration information. Further, JP Patent Publication (Unexamined Application) No. 11-215135 discloses a method of managing the quality of individual communication paths in a wireless network comprised of a plurality of nodes. In this example, a hub station is selected from among the multiple nodes, and the hub station centrally manages the communication path quality information in the wireless network. Each node in the wireless network transmits its own management information to all of the other nodes. Each node receives the management information from all of the other nodes in the wireless network and evaluates it. The nodes then transmit management information results to the hub station, which in turn overwrites this information on the communication quality information table. This example is wireless and involves only communication quality information.
These conventional node configuration information management methods have the following problems. In the communication apparatus disclosed in JP Patent Publication (Unexamined Application) No. 11-88396, each time the node configuration is updated as the number of nodes increases, node configuration information corresponding to the number of nodes must be transmitted. This results in an increase in overhead. Further, the hub station must wait until it receives an Ack signal from all of the nodes to which the hub station has transmitted.
While this management method creates no problems in the case of wired examples, it would not be an efficient method for wireless communication with limited frequency resources, because no other data can be transmitted while waiting for an Ack signal. Further, in a wired environment using cables, for example, the communication conditions among the nodes are fixed, so in this case there is no need to recognize the communication quality conditions. For these reasons, there is no description of a method of managing communication quality information. On the other hand, JP Patent Publication (Unexamined Application) No. 11-215135, which relates to a wireless communication method, does not describe the method of managing node configuration information. It is possible to transmit node configuration information by adding it to the above-described communication quality information. However, while the communication quality information varies depending on communication conditions, node configuration information is updated upon registration of a new node, deletion of a node, or when there is a change in a node. Accordingly, inserting the node configuration information in each frame and thus notifying the hub station would be redundant and could not be called an efficient method for wireless communication with limited frequency resources.
In view of these problems of the prior art, it is an object of the invention to provide a node configuration information management method and a wireless network system whereby node configuration information in a wireless bus comprised of a hub station and multiple nodes is managed by the hub station in a centralized manner. This is carried out in a manner such that the hub station can share the latest node configuration information with all of the nodes.
It is another object of the invention to provide a node configuration information management method and a wireless network system whereby node configuration information in a wireless bus comprised of a hub station and multiple nodes is centrally managed by the hub station in each frame. This is carried out in a manner such that the hub station can share the latest node configuration information with all of the nodes in the wireless bus within a minimum frame.